Power couplers, notably bidirectional ones, used in radiofrequency transmitters make it possible to check the transmitted power by sampling a fraction of the signal. For this purpose, they are for example disposed at the output of a power amplifier. Bidirectional couplers make it possible to check both the incident input power and the power reflected by a load, for example an antenna. Bidirectional power couplers commonly have the function of coupling a secondary line—or measuring line—to the transmission line by the intermediary of transformers.
Bidirectional power couplers are therefore notably found at the output of RF or microwave frequency amplifiers, for example on amplification boards equipping radio transmitters and HF terminals, with operating frequencies of the order of one MHz to several tens of MHz, or in radar transmitters operating in much higher frequency ranges.
The use of such couplers makes it possible to check the correct functioning of amplifiers by diagnosing the presence or absence of output power, or even to determine a standing wave ratio, or S.W.R., by measuring the reflected power. Such information makes it possible to trigger possible alarms in the case of malfunction, or even to carry out a control of the operating parameters of the load.
Bidirectional power couplers have been proposed, using transformers formed by wire windings on cores of ferromagnetic material. Notably, a bidirectional power coupler has been proposed comprising a ferrite core with two cylindrical cavities, or binocular ferrite core, each of these cavities being wound with a wire winding, the winding thus extending over the inside surface of the cavities and the outside surface of the ferrite core. The American patent published under the reference U.S. Pat. No. 6,114,924 proposes an alternative construction of such a coupler, having two binocular ferrite cores placed back-to-back, allowing the winding to extend essentially over the inside surface of the cavities.
However, such coupler structures are produced by skilled small-scale production, which essentially has an effect on their manufacturing cost and possibly on the reproducibility and quality of performance, notably in terms of losses and coupling directivity. Moreover, this production imposes the manual application and soldering of the coupler onto the board it equips.